The present disclosure relates to an electric power tool for performing on-off control of a motor by gripping a switch lever disposed in a grip, and particularly to the electric power tool for improving a switch mechanism.
As an example of a portable electric power tool, a disk grinder is known as described in JP-A-2005-246542. FIG. 13 is a sectional view showing the whole structure of a related disk grinder. A disk grinder 101 has a cylindrical motor housing 102 for receiving a motor 106 which is a driving source. A tail cover 103 of a left and right division type is disposed in the back of the motor housing 102, and a power cord 117 is connected from the tail cover 103 to the outside. A gear cover 104 for receiving a power transmission mechanism configured to include two sets of bevel gears 108, 109 for converting a power transmission direction by a rotating shaft of the motor by about 90° is disposed in the front of the motor housing 102. A grindstone 105 is attached to a spindle 110 which is connected to the bevel gear 109 and downward protrudes from the gear cover 104.
A switch mechanism for turning on and off the motor 106 is disposed under the tail cover 103. The switch mechanism is configured to include a switch 115, a switch lever 121 for pushing a plunger 115a of the switch 115 and an off-lock lever 123 for holding the switch lever 121 in a constant state. The switch lever 121 can swing around a turning shaft 125 by a minute angle, and a worker grips the tail cover 103 together with the switch lever 121 and thereby, the switch lever 121 swings in a direction of arrow 131 in the drawing. When the switch lever 121 swings, a push bar part 121a which is disposed integrally to the switch lever 121 and is opposed to the plunger 115a pushes the plunger 115a and thereby, the switch 115 changes to an on state. In order to turn off rotation of the motor 106, the worker releases the switch lever 121 and thereby, the switch lever 121 returns to the original position (a position shown in FIG. 13) by action of a spring 126.
In recent years, international standards for electric power tools require safety measures in which the switch lever 121 can be gripped only when some action is taken so that the motor 106 does not rotate by only gripping the switch lever 121. Because of that, the disk grinder 101 is constructed so that the off-lock lever 123 capable of sliding backward and forward is disposed in the vicinity of substantially the center of the switch lever 121 and the switch lever 121 can be moved in the direction of arrow 131 in only a state of sliding this off-lock lever 123 in a direction of arrow 132 (the front). As a result, a protrusion 123a (see FIG. 14) is disposed in the off-lock lever 123 and a rib 133 is disposed in the opposed portion of the tail cover 103. In a state in which the worker does not touch the switch lever 121, the off-lock lever 123 is positioned backward (a direction opposite to the arrow 132) by action of a spring 124 and in this case, the protrusion 123a runs on the rib 133, so that the switch lever 121 cannot be moved in the direction of arrow 131.
When the worker grips the switch lever 121, the off-lock lever 123 is first moved in the direction of arrow 132 and the switch lever 121 is gripped with a moved state held and the switch lever 121 is swung in the direction of arrow 131. A state of gripping this switch lever 121 is shown in FIG. 14. In the state of gripping the switch lever 121, the switch lever 121 swings around the turning shaft 125 clockwise and the switch lever 121 abuts on a lower surface of the tail cover 103. In this case, the off-lock lever 123 is moved forward while compressing the spring 124, so that a state of abutting of the protrusion 123a on the rib 133 is released. By sliding the off-lock lever 123 thus, the switch lever 121 can swing around the turning shaft 125 and the push bar part 121a pushes the plunger 115a and thereby, the switch 115 can be turned on.
When the switch 115 is turned on, AC electric power is supplied to the motor 106 through the switch 115 and a rotor rotates and thereby, the grindstone 105 is rotated and intended work can be done. In this case, a cooling fan 107 disposed in a rotating shaft 106a of the motor 106 rotates and an airflow for cooling of the motor 106 is generated inside the motor housing 102. In order to turn off the switch 115, when the worker releases a grip of the switch lever 121, the switch lever 121 returns to the state of FIG. 13 by a repulsive force of the spring 126 and the switch 115 is turned off.
As described above, the conventional disk grinder 101 is constructed so that a spring force is always applied to the switch lever 121 to the off side by the spring 126 and similarly a spring force is always applied to the off-lock lever 123 to the off side by the spring 124 and the switch 115 cannot be turned on by being disturbed by the rib 133 disposed in the tail cover 103 even when the switch lever 121 is gripped simply. Then, when the off-lock lever 123 is slid forward against the spring force of the spring 124, the switch 115 can be turned on by being released from an obstacle of the rib 133.